Bunions have long been one of the more common types of painful foot deformities. The technical name for this type of deformity is Hallux Abducto Valgus (HAV), which is generally described as a medial deviation of the first metatarsal accompanied by a lateral deviation and/or valgus rotation of the hallux (or “big toe”). The result effect is a subluxation of the big toe joint (or first metatarsophalangeal joint (MTPJ)) creating a boney prominence (or eminence) on the inside of the foot, near the base of the big toe. FIG. 1A illustrates the normal anatomical configuration of a left human foot, which includes the first metatarsal 10 that extends between the medial cuneiform 12 and the hallux 13. The first metatarsal 10 articulates with the medial cuneiform 12 at the first metatarsocuneiform joint 14 at its most proximal aspect; and is further connected to the hallux 13 at the metatarsophalangeal joint 15 at its most distal aspect. Located adjacent (lateral) to the first metatarsal 10 is the second metatarsal 16, which articulates with the intermediate cuneiform 17 at the second metatarsocuneiform joint 18. The joint between the medial cuneiform 12 and intermediate cuneiform 17 is the intermetatarsocuneiform joint 18. The sesamoids 19 are located beneath (plantar to) the first metatarsal head at the first MTPJ, and articulates with the head of the first metatarsal.
FIG. 1B illustrates the resulting anatomical configuration of a human foot experiencing HAV. In particular, the first metatarsal 10 extends from the medial cuneiform 12 and deviates medially while the hallux 13 deviates laterally. As a result, the sesamoids 19 may rotate with the first metatarsal 10. This condition may lead to painful motion of the big toe joint and/or difficulty fitting footwear. Other conditions associated with HAV may include: hammer toe formation of the adjacent toes, forefoot pain on the ball of the foot (aka metatarsalgia), stress fractures of the adjacent metatarsals, flat feet (pes planus), and arthritis of the first MTPJ or midfoot.
Bunions may occur from a variety of causes, such as genetic factors, gender influences, biomechanical and structural causes, trauma (injury), and certain shoes. Some physicians believe genetics play a large role in the development of bunions. Dudley Morton suggested that bunions may be a result of evolutionary influence, and described a certain foot type that is associated with bunions—the so called Morton's foot (a condition where the first metatarsal is shorter than the other metatarsals. See Morton D J. The Human Foot: Its evolution, Physiology and functional Disorders. Columbia University Press, Morningside Heights, N.Y., 1935. Some people develop bunions when associated with a condition called hypermobility, where the midfoot (i.e., metatarsocuneiform joint or “MCJ,” illustrated in FIG. 1A as the joint defined at the meeting of the metatarsal 10 and the cuneiform 12) exhibits excessive motion. Less commonly, malshaped bones (hallux and/or first metatarsal) may give the appearance of and/or cause bunions. Many physicians attribute the progressive development of bunions to high heel and pointy toe shoes more commonly worn by women. It is well known that women are more likely to develop bunions than men.
Surgeons use weightbearing radiographs to determine the severity of HAV in an attempt to quantity the deformity, and aid in surgical decision making. The most commonly utilized radiographic measurement is the intermetatarsal angle (IMA), which measures the angle between a longitudinal bisection of the first and second metatarsal shafts. The IMA essentially measures the extent with which the first metatarsal has deviated (medially) from the second metatarsal. The normal value for the IMA is less than 8 degrees. Another useful radiographic measurement is the hallux abductus angle (HAA), which measures the amount of lateral deviation of the big toe (hallux). The HAA essentially measures the extent with which the hallux has deviated (laterally) from its native position (nearly rectus with the more proximal metatarsal). The normal value for the HAA is less than 12 degrees. A patient with a mild HAV deformity may have an IMA of 10-12 degrees and an HAA of 21-30 degrees. A patient with a moderate HAV deformity may have an IMA of 12-16 degrees and an HAA of 31-40 degrees. A patient with a severe HAV deformity may have an IMA of greater than 16 degrees and an HAA of greater than 40 degrees.
Various techniques have been developed to surgically correct HAV. The most basic technique simply involves resecting any enlarged bone at the medial aspect of the first metatarsal head, but this approach is typically used in conjunction with other more advanced techniques. A common technique involves an osteotomy (bone cut) procedure in which the first metatarsal is broken into two pieces and the distal portion of the bone is translated closer (medially) to the adjacent second metatarsal. The osteotomy may be performed at several locations on the first metatarsal, depending on the severity of the deformity. Less severe HAV deformities are typically corrected with an osteotomy near the head (10a in FIG. 1) of the first metatarsal, whereas moderate and larger deformities are corrected with an osteotomy near the base (10b in FIG. 1) of the first metatarsal. Whichever osteotomy technique is utilized, only the distal portion of the first metatarsal is relocated into a more lateral position while the proximal segment position remains unchanged. It should be understood that any osteotomy procedure reorients the first metatarsal by changing its shape from that of a straight bone to a more curved bone.
Alternative techniques have been developed that do not require breaking of the bone, or changing the natural shape of the first metatarsal. One such technique calls for fusion of the MCJ, wherein the entire first metatarsal is relocated into a corrected position. This approach was originally developed by Dr. Paul Lapidus, and hence this particular technique is often referred to as the Lapidus approach (or Lapidus Bunionectomy or Lapidus Arthrodesis or Modified Lapidus Bunionectomy/Arthrodesis). In some situations the procedure may involve an isolated fusion of the 1st MCJ, and in other situations surgeons may also incorporate a fusion of the intermediate cueniform area and or 2nd metatarsal base. In general, the idea behind the Lapidus approach is to permanently fuse the base of the first metatarsal to the medial cuneiform bone in a corrected new position. This permanent fixation is carried out by first reducing the IMA and then fusing the MCJ. Implementation of this approach often involves the use of a number of screws across the joint or a plate that can accommodate screws to attach the plate to the metatarsal and medial cuneiform. In some cases, a fusion of the 1st MCJ that incorporates lengthening of the entire segment by adding bone graft (i.e., a block of bone) into the fusion site is better termed a distraction Lapidus.